The present invention relates to network devices and network signals. In particular, the present invention is a method and device for associating a signal measured on a network with a communication device connected to the network.
In a typical industrial plant, a distributed control system (DCS) is used to control many of the industrial processes performed at the plant. Typically, the plant has a centralized control room having a computer system with user input/output (I/O), disc I/O, and other peripherals as are known in the computing art. Coupled to the computing system are a controller and a process I/O subsystem.
The process I/O subsystem includes I/O ports which are connected to various field devices throughout the plant. Field devices include various types of analytical equipment, silicon pressure sensors, capacitive pressure sensors, resistive temperature detectors, thermocouples, strain gauges, limit switches, on/off switches, flow transmitters, pressure transmitters, capacitance level switches, weigh scales, transducers, valve positioners, valve controllers, actuators, solenoids, and indicator lights. The term “field device” encompasses these devices, as well as any other device that performs a function in a distributed control system.
Fieldbus is a multi-drop serial digital two-way communications protocol intended for connecting field instruments and other process devices such as monitoring and simulation units in distributed control systems. Fieldbus allows enhanced digital communication over previous process control loop methods while maintaining the ability to power process devices coupled to the Fieldbus loop and while meeting intrinsic safety requirements.
Two reasonably standardized industrial Fieldbus protocols are Foundation Fieldbus and Profibus. The physical layer of the Fieldbus protocols are defined by Instrument Society of America (ISA) standard ANSI/ISA-50.02-1992, and its draft two extension dated 1995. The Fieldbus protocol defines two subprotocols. An H1 Fieldbus network transmits data at a rate up to 31.25 kilobits per second (Kbps) and provides power to field devices coupled to the network. The H1 physical layer subprotocol is defined in Clause 11 of Part 2 of the ISA standard, approved in September 1992. An H2 Fieldbus network transmits data at a rate up to 2.5 megabits per second (Mbps), does not provide power to field devices connected to the network, and is provided with redundant transmission media.
The signals sent by devices communicating on a network may be used to indicate whether the devices are operating normally. For instance, certain signal measurements, such as a signal's amplitude, aid in diagnosing a problem with one of the communicating devices. Traditionally, an oscilloscope is used to measure the signals of devices communicating on the network. However, these signals cannot easily be associated with the devices of origin using an oscilloscope, which makes it difficult not only to track the devices currently communicating on the network, but also to identify which device has a problem.